The present invention relates to a method of purification of phenol, and in particular, to a method of purification of phenol which is produced within joint phenol and acetone production by the cumene oxidation method.
The cumene-to-phenol industrial method is well known and involves a two step synthesis: air-oxidation of cumene to a cumene hydroperoxide (CHP) intermediate, followed by acidic decomposition (cleavage) of the CHP to yield phenol and acetone as principle products. However, in addition to the desired products, the resulting crude cleavage product mixture also contains amounts of various by-products including, alphamethylstyrene, acetophenone, cumylphenol, unreacted cumene and traces of various xe2x80x9ccarbonyl-typexe2x80x9d impurities including hydroxyacetone, mesityl oxide and aldehydes. During the subsequent purification steps these undesirable by-products and impurities must be removed from the final product phenol and acetone using various separation methods which include extraction, distillation and catalytic chemical treatment.
The above mentioned xe2x80x9ccarbonyl-typexe2x80x9d impurities are particularly difficult to remove from phenol by conventional distillation methods, and a chemical treatment of the crude phenol stream is typically required for their efficient removal. Trace amounts of carbonyl-type impurities such as hydroxyacetone and mesityl oxide have color-forming tendencies, and their presence in final phenol product, even in minute amounts, render its quality unsuitable for critical end use applications such as bisphenol A and polycarbonate.
U.S. Pat. No. 3,029,294, U.S. Pat. No. 3,454,653, U.S. Pat. No. 5,414,154 and U.S. Pat. No. 5,502,259 describe phenol purification from carbonyl-type impurities using various solid heterogeneous acid catalysts, of which the most widely used commercially is an acidic cation-exchange resin such as Amberlyst 15 (Rohm and Haas) or Lewatit 2431 (Bayer). These acidic ion-exchange resin catalysts are commonly used as packed beds of small polymeric beads composed of sulfonated polystyrene cross-linked with divinylbenzene and being of either gellular or macroreticular type.
In these catalytic treatment processes the crude phenol stream is continuously passed through a fixed bed of the solid acidic ion-exchange resin (IER) held at elevated temperature. The trace carbonyl-type impurities present in the stream react with phenol under these conditions to form higher boiling derivatives, which can subsequently be easily removed from phenol via conventional distillation.
These cationic IER-treatment processes are generally quite efficient for the removal of carbonyls from phenol via promoting the condensation reactions. However, during the course of the treatment, small microscopic sulfonic acid fragments (oligomers) leach from the solid IER catalyst to contaminate the effluent phenol stream. These acidic oligomer contaminants must be removed from the phenol or they will cause downstream product quality and equipment corrosion issues.
In the current art this oligomer leaching problem is combated by adding a base such as sodium hydroxide to the IER-treated effluent stream. The added sodium hydroxide base dissolves in the phenol stream, neutralizes the traces of acidic oligomers present, and stabilizes the color of the product phenol produced from the downstream distillations. However, it has been found that the addition of sodium hydroxide or other soluble bases to the phenol stream has the following disadvantages:
The strongly basic sodium hydroxide reacts with the phenol itself in addition to the oligomers to form a sodium phenolate salt. This phenolate salt must be recovered or a loss in phenol yield will result;
The sodium phenolate salt can cause fouling of heat exchanger surfaces resulting in downtime and lost production; and
The sodium phenolate salt can contaminate the final product phenol during the subsequent distillation process causing poor quality product and color.
Another method for combating the oligomer leaching problem is taught (U.S. Pat. No. 4,847,433, U.S. Pat. No. 4,876,395) which adds a solid basic material such as barium carbonate directly into the process to scavenge acidic oligomers. However, dissolution of solid basic reagents of this sort in the phenol streams is poor. As a result, a non-homogeneous mixture results, causing downstream processing problems such as plugging of heat exchangers. A fixed-bed approach to scavenging the acidic oligomers is definitely preferable to addition of basic substances such as sodium hydroxide or barium carbonate into the process stream.
In U.S. Pat. No. 4,191,843, U.S. Pat. No. 4,766,254 and U.S. Pat. No. 5,288,926 another method is taught to remove leached acidic oligomer contaminants from phenol streams by continuously passing the stream through a packed bed of solid basic ion exchange resin. These polymeric resins are composed of a polystyrene-divinylbenzene backbone containing amine or quaternary ammonium active groups. However, these anion exchange resins are expensive and inherently unstable at operating temperatures above 100xc2x0 C. As a result, their applications are limited by temperature, their lifetime of effective use is short, and they must be replaced frequently, which is expensive. Also, it has been discovered that these anion exchange resins are ultimately ineffective since they release their own oligomers of an alkaline nature which contaminate the downstream process causing product quality problems.
In U.S. Pat. No. 5,008,470 and U.S. Pat. No. 5,105,026 another method is taught to remove leached acidic oligomer contaminants using fixed beds of amphoteric solid inorganic materials containing titanium and zirconium. Such weakly basic adsorbants are expensive and must be replaced frequently because their adsorption capacity is quite limited.
Therefore an improved method is needed for scavenging of acidic oligomer contaminants from phenol streams which have been previously treated with cation exchange resin catalysts.
It has been discovered that layered double hydroxides (LDHs) can be effectively employed as basic adsorbents to scavenge acidic oligomer contaminants from phenol streams previously treated with ion exchange resin. Thus, in accordance with the invention, a process for separating sulfonic acid compounds from a phenolic solvent is provided by contacting the phenolic solvent with a layered double hydroxide composition. Preferably, the LDH is a hydrotalcite-type material (HTM) of the formula:
[MII1-xMIIIx(OH)2](Anxe2x88x92)x/n
or a hydrate thereof, wherein MII is a divalent metal cation, MIII is a trivalent metal cation, A is an interlayer anion of charge nxe2x88x92, and x is from 0.12 to 0.8. The process can be applied in the conventional industrial process for converting cumene to phenol to remove sulfonic acid compounds from the phenol product. A process and a facility for producing purified phenol by converting cumene to phenol are provided. In the conversion of cumene to phenol, the phenol often contains carbonyl-type impurities. The phenol and carbonyl-type impurities are reacted in the presence of an ion exchange resin catalyst (IER) to produce a reaction product that may contain sulfonic acid compounds. The reaction product is contacted with an HTM to reduce the amount of sulfonic acid compounds which may be present and to produce a purified phenol-containing stream. The purified phenol-containing stream may be further purified using conventional separation techniques, such as distillation.